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Linus Torvalds1da177e2005-04-16 15:20:36 -07001
2 How to Get Your Change Into the Linux Kernel
3 or
4 Care And Operation Of Your Linus Torvalds
5
6
7
8For a person or company who wishes to submit a change to the Linux
9kernel, the process can sometimes be daunting if you're not familiar
10with "the system." This text is a collection of suggestions which
11can greatly increase the chances of your change being accepted.
12
Randy Dunlapbc7455f2006-07-30 03:03:45 -070013Read Documentation/SubmitChecklist for a list of items to check
14before submitting code. If you are submitting a driver, also read
15Documentation/SubmittingDrivers.
Linus Torvalds1da177e2005-04-16 15:20:36 -070016
17
18
19--------------------------------------------
20SECTION 1 - CREATING AND SENDING YOUR CHANGE
21--------------------------------------------
22
23
24
251) "diff -up"
26------------
27
28Use "diff -up" or "diff -uprN" to create patches.
29
30All changes to the Linux kernel occur in the form of patches, as
31generated by diff(1). When creating your patch, make sure to create it
32in "unified diff" format, as supplied by the '-u' argument to diff(1).
33Also, please use the '-p' argument which shows which C function each
34change is in - that makes the resultant diff a lot easier to read.
35Patches should be based in the root kernel source directory,
36not in any lower subdirectory.
37
38To create a patch for a single file, it is often sufficient to do:
39
Randy Dunlap84da7c02005-06-28 20:45:30 -070040 SRCTREE= linux-2.6
Linus Torvalds1da177e2005-04-16 15:20:36 -070041 MYFILE= drivers/net/mydriver.c
42
43 cd $SRCTREE
44 cp $MYFILE $MYFILE.orig
45 vi $MYFILE # make your change
46 cd ..
47 diff -up $SRCTREE/$MYFILE{.orig,} > /tmp/patch
48
49To create a patch for multiple files, you should unpack a "vanilla",
50or unmodified kernel source tree, and generate a diff against your
51own source tree. For example:
52
Randy Dunlap84da7c02005-06-28 20:45:30 -070053 MYSRC= /devel/linux-2.6
Linus Torvalds1da177e2005-04-16 15:20:36 -070054
Randy Dunlap84da7c02005-06-28 20:45:30 -070055 tar xvfz linux-2.6.12.tar.gz
56 mv linux-2.6.12 linux-2.6.12-vanilla
57 diff -uprN -X linux-2.6.12-vanilla/Documentation/dontdiff \
58 linux-2.6.12-vanilla $MYSRC > /tmp/patch
Linus Torvalds1da177e2005-04-16 15:20:36 -070059
60"dontdiff" is a list of files which are generated by the kernel during
61the build process, and should be ignored in any diff(1)-generated
Randy Dunlap84da7c02005-06-28 20:45:30 -070062patch. The "dontdiff" file is included in the kernel tree in
632.6.12 and later. For earlier kernel versions, you can get it
64from <http://www.xenotime.net/linux/doc/dontdiff>.
Linus Torvalds1da177e2005-04-16 15:20:36 -070065
66Make sure your patch does not include any extra files which do not
67belong in a patch submission. Make sure to review your patch -after-
68generated it with diff(1), to ensure accuracy.
69
70If your changes produce a lot of deltas, you may want to look into
71splitting them into individual patches which modify things in
Randy Dunlap84da7c02005-06-28 20:45:30 -070072logical stages. This will facilitate easier reviewing by other
Linus Torvalds1da177e2005-04-16 15:20:36 -070073kernel developers, very important if you want your patch accepted.
Randy Dunlap84da7c02005-06-28 20:45:30 -070074There are a number of scripts which can aid in this:
Linus Torvalds1da177e2005-04-16 15:20:36 -070075
76Quilt:
77http://savannah.nongnu.org/projects/quilt
78
Linus Torvalds1da177e2005-04-16 15:20:36 -070079Andrew Morton's patch scripts:
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -080080http://www.zip.com.au/~akpm/linux/patches/
81Instead of these scripts, quilt is the recommended patch management
82tool (see above).
Randy Dunlap84da7c02005-06-28 20:45:30 -070083
84
Linus Torvalds1da177e2005-04-16 15:20:36 -070085
862) Describe your changes.
87
88Describe the technical detail of the change(s) your patch includes.
89
90Be as specific as possible. The WORST descriptions possible include
91things like "update driver X", "bug fix for driver X", or "this patch
92includes updates for subsystem X. Please apply."
93
94If your description starts to get long, that's a sign that you probably
95need to split up your patch. See #3, next.
96
97
98
993) Separate your changes.
100
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800101Separate _logical changes_ into a single patch file.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700102
103For example, if your changes include both bug fixes and performance
104enhancements for a single driver, separate those changes into two
105or more patches. If your changes include an API update, and a new
106driver which uses that new API, separate those into two patches.
107
108On the other hand, if you make a single change to numerous files,
109group those changes into a single patch. Thus a single logical change
110is contained within a single patch.
111
112If one patch depends on another patch in order for a change to be
113complete, that is OK. Simply note "this patch depends on patch X"
114in your patch description.
115
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800116If you cannot condense your patch set into a smaller set of patches,
117then only post say 15 or so at a time and wait for review and integration.
118
119
Linus Torvalds1da177e2005-04-16 15:20:36 -0700120
1214) Select e-mail destination.
122
123Look through the MAINTAINERS file and the source code, and determine
124if your change applies to a specific subsystem of the kernel, with
125an assigned maintainer. If so, e-mail that person.
126
127If no maintainer is listed, or the maintainer does not respond, send
128your patch to the primary Linux kernel developer's mailing list,
129linux-kernel@vger.kernel.org. Most kernel developers monitor this
130e-mail list, and can comment on your changes.
131
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800132
133Do not send more than 15 patches at once to the vger mailing lists!!!
134
135
Linus Torvalds1da177e2005-04-16 15:20:36 -0700136Linus Torvalds is the final arbiter of all changes accepted into the
Linus Torvalds99ddcc72007-01-23 14:22:35 -0800137Linux kernel. His e-mail address is <torvalds@linux-foundation.org>.
138He gets a lot of e-mail, so typically you should do your best to -avoid-
139sending him e-mail.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700140
141Patches which are bug fixes, are "obvious" changes, or similarly
142require little discussion should be sent or CC'd to Linus. Patches
143which require discussion or do not have a clear advantage should
144usually be sent first to linux-kernel. Only after the patch is
145discussed should the patch then be submitted to Linus.
146
Linus Torvalds1da177e2005-04-16 15:20:36 -0700147
148
1495) Select your CC (e-mail carbon copy) list.
150
151Unless you have a reason NOT to do so, CC linux-kernel@vger.kernel.org.
152
153Other kernel developers besides Linus need to be aware of your change,
154so that they may comment on it and offer code review and suggestions.
155linux-kernel is the primary Linux kernel developer mailing list.
156Other mailing lists are available for specific subsystems, such as
157USB, framebuffer devices, the VFS, the SCSI subsystem, etc. See the
158MAINTAINERS file for a mailing list that relates specifically to
159your change.
160
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800161Majordomo lists of VGER.KERNEL.ORG at:
162 <http://vger.kernel.org/vger-lists.html>
163
Paul Jackson1caf1f02005-07-31 22:34:48 -0700164If changes affect userland-kernel interfaces, please send
165the MAN-PAGES maintainer (as listed in the MAINTAINERS file)
166a man-pages patch, or at least a notification of the change,
167so that some information makes its way into the manual pages.
168
Linus Torvalds1da177e2005-04-16 15:20:36 -0700169Even if the maintainer did not respond in step #4, make sure to ALWAYS
170copy the maintainer when you change their code.
171
172For small patches you may want to CC the Trivial Patch Monkey
Kees Cookf62870d2006-01-03 13:33:31 +0100173trivial@kernel.org managed by Adrian Bunk; which collects "trivial"
Linus Torvalds1da177e2005-04-16 15:20:36 -0700174patches. Trivial patches must qualify for one of the following rules:
175 Spelling fixes in documentation
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700176 Spelling fixes which could break grep(1)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700177 Warning fixes (cluttering with useless warnings is bad)
178 Compilation fixes (only if they are actually correct)
179 Runtime fixes (only if they actually fix things)
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700180 Removing use of deprecated functions/macros (eg. check_region)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700181 Contact detail and documentation fixes
182 Non-portable code replaced by portable code (even in arch-specific,
183 since people copy, as long as it's trivial)
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700184 Any fix by the author/maintainer of the file (ie. patch monkey
Linus Torvalds1da177e2005-04-16 15:20:36 -0700185 in re-transmission mode)
Kees Cookf62870d2006-01-03 13:33:31 +0100186URL: <http://www.kernel.org/pub/linux/kernel/people/bunk/trivial/>
Randy Dunlap84da7c02005-06-28 20:45:30 -0700187
Linus Torvalds1da177e2005-04-16 15:20:36 -0700188
189
190
1916) No MIME, no links, no compression, no attachments. Just plain text.
192
193Linus and other kernel developers need to be able to read and comment
194on the changes you are submitting. It is important for a kernel
195developer to be able to "quote" your changes, using standard e-mail
196tools, so that they may comment on specific portions of your code.
197
198For this reason, all patches should be submitting e-mail "inline".
199WARNING: Be wary of your editor's word-wrap corrupting your patch,
200if you choose to cut-n-paste your patch.
201
202Do not attach the patch as a MIME attachment, compressed or not.
203Many popular e-mail applications will not always transmit a MIME
204attachment as plain text, making it impossible to comment on your
205code. A MIME attachment also takes Linus a bit more time to process,
206decreasing the likelihood of your MIME-attached change being accepted.
207
208Exception: If your mailer is mangling patches then someone may ask
209you to re-send them using MIME.
210
211
Kirill Korotaev683e91c2006-09-29 02:01:47 -0700212WARNING: Some mailers like Mozilla send your messages with
213---- message header ----
214Content-Type: text/plain; charset=us-ascii; format=flowed
215---- message header ----
216The problem is that "format=flowed" makes some of the mailers
217on receiving side to replace TABs with spaces and do similar
218changes. Thus the patches from you can look corrupted.
219
220To fix this just make your mozilla defaults/pref/mailnews.js file to look like:
221pref("mailnews.send_plaintext_flowed", false); // RFC 2646=======
222pref("mailnews.display.disable_format_flowed_support", true);
223
224
Linus Torvalds1da177e2005-04-16 15:20:36 -0700225
2267) E-mail size.
227
228When sending patches to Linus, always follow step #6.
229
230Large changes are not appropriate for mailing lists, and some
231maintainers. If your patch, uncompressed, exceeds 40 kB in size,
232it is preferred that you store your patch on an Internet-accessible
233server, and provide instead a URL (link) pointing to your patch.
234
235
236
2378) Name your kernel version.
238
239It is important to note, either in the subject line or in the patch
240description, the kernel version to which this patch applies.
241
242If the patch does not apply cleanly to the latest kernel version,
243Linus will not apply it.
244
245
246
2479) Don't get discouraged. Re-submit.
248
249After you have submitted your change, be patient and wait. If Linus
250likes your change and applies it, it will appear in the next version
251of the kernel that he releases.
252
253However, if your change doesn't appear in the next version of the
254kernel, there could be any number of reasons. It's YOUR job to
255narrow down those reasons, correct what was wrong, and submit your
256updated change.
257
258It is quite common for Linus to "drop" your patch without comment.
259That's the nature of the system. If he drops your patch, it could be
260due to
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700261* Your patch did not apply cleanly to the latest kernel version.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700262* Your patch was not sufficiently discussed on linux-kernel.
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700263* A style issue (see section 2).
264* An e-mail formatting issue (re-read this section).
265* A technical problem with your change.
266* He gets tons of e-mail, and yours got lost in the shuffle.
267* You are being annoying.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700268
269When in doubt, solicit comments on linux-kernel mailing list.
270
271
272
27310) Include PATCH in the subject
274
275Due to high e-mail traffic to Linus, and to linux-kernel, it is common
276convention to prefix your subject line with [PATCH]. This lets Linus
277and other kernel developers more easily distinguish patches from other
278e-mail discussions.
279
280
281
28211) Sign your work
283
284To improve tracking of who did what, especially with patches that can
285percolate to their final resting place in the kernel through several
286layers of maintainers, we've introduced a "sign-off" procedure on
287patches that are being emailed around.
288
289The sign-off is a simple line at the end of the explanation for the
290patch, which certifies that you wrote it or otherwise have the right to
291pass it on as a open-source patch. The rules are pretty simple: if you
292can certify the below:
293
Linus Torvaldscbd83da2005-06-13 17:51:55 -0700294 Developer's Certificate of Origin 1.1
Linus Torvalds1da177e2005-04-16 15:20:36 -0700295
296 By making a contribution to this project, I certify that:
297
298 (a) The contribution was created in whole or in part by me and I
299 have the right to submit it under the open source license
300 indicated in the file; or
301
302 (b) The contribution is based upon previous work that, to the best
303 of my knowledge, is covered under an appropriate open source
304 license and I have the right under that license to submit that
305 work with modifications, whether created in whole or in part
306 by me, under the same open source license (unless I am
307 permitted to submit under a different license), as indicated
308 in the file; or
309
310 (c) The contribution was provided directly to me by some other
311 person who certified (a), (b) or (c) and I have not modified
312 it.
313
Linus Torvaldscbd83da2005-06-13 17:51:55 -0700314 (d) I understand and agree that this project and the contribution
315 are public and that a record of the contribution (including all
316 personal information I submit with it, including my sign-off) is
317 maintained indefinitely and may be redistributed consistent with
318 this project or the open source license(s) involved.
319
Linus Torvalds1da177e2005-04-16 15:20:36 -0700320then you just add a line saying
321
Alexey Dobriyan9fd55592005-06-25 14:59:34 -0700322 Signed-off-by: Random J Developer <random@developer.example.org>
Linus Torvalds1da177e2005-04-16 15:20:36 -0700323
Greg KHaf45f322006-09-12 20:35:52 -0700324using your real name (sorry, no pseudonyms or anonymous contributions.)
325
Linus Torvalds1da177e2005-04-16 15:20:36 -0700326Some people also put extra tags at the end. They'll just be ignored for
327now, but you can do this to mark internal company procedures or just
328point out some special detail about the sign-off.
329
330
Paul Jackson75f84262005-10-02 18:01:42 -070033112) The canonical patch format
Randy Dunlap84da7c02005-06-28 20:45:30 -0700332
Paul Jackson75f84262005-10-02 18:01:42 -0700333The canonical patch subject line is:
334
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700335 Subject: [PATCH 001/123] subsystem: summary phrase
Paul Jackson75f84262005-10-02 18:01:42 -0700336
337The canonical patch message body contains the following:
338
339 - A "from" line specifying the patch author.
340
341 - An empty line.
342
343 - The body of the explanation, which will be copied to the
344 permanent changelog to describe this patch.
345
346 - The "Signed-off-by:" lines, described above, which will
347 also go in the changelog.
348
349 - A marker line containing simply "---".
350
351 - Any additional comments not suitable for the changelog.
352
353 - The actual patch (diff output).
354
355The Subject line format makes it very easy to sort the emails
356alphabetically by subject line - pretty much any email reader will
357support that - since because the sequence number is zero-padded,
358the numerical and alphabetic sort is the same.
359
Paul Jacksond6b9acc2005-10-03 00:29:10 -0700360The "subsystem" in the email's Subject should identify which
361area or subsystem of the kernel is being patched.
362
363The "summary phrase" in the email's Subject should concisely
364describe the patch which that email contains. The "summary
365phrase" should not be a filename. Do not use the same "summary
366phrase" for every patch in a whole patch series.
367
368Bear in mind that the "summary phrase" of your email becomes
369a globally-unique identifier for that patch. It propagates
370all the way into the git changelog. The "summary phrase" may
371later be used in developer discussions which refer to the patch.
372People will want to google for the "summary phrase" to read
373discussion regarding that patch.
374
375A couple of example Subjects:
376
377 Subject: [patch 2/5] ext2: improve scalability of bitmap searching
378 Subject: [PATCHv2 001/207] x86: fix eflags tracking
Paul Jackson75f84262005-10-02 18:01:42 -0700379
380The "from" line must be the very first line in the message body,
381and has the form:
382
383 From: Original Author <author@example.com>
384
385The "from" line specifies who will be credited as the author of the
386patch in the permanent changelog. If the "from" line is missing,
387then the "From:" line from the email header will be used to determine
388the patch author in the changelog.
389
390The explanation body will be committed to the permanent source
391changelog, so should make sense to a competent reader who has long
392since forgotten the immediate details of the discussion that might
393have led to this patch.
394
395The "---" marker line serves the essential purpose of marking for patch
396handling tools where the changelog message ends.
397
398One good use for the additional comments after the "---" marker is for
399a diffstat, to show what files have changed, and the number of inserted
400and deleted lines per file. A diffstat is especially useful on bigger
401patches. Other comments relevant only to the moment or the maintainer,
402not suitable for the permanent changelog, should also go here.
Randy Dunlap58591e82006-01-08 01:04:52 -0800403Use diffstat options "-p 1 -w 70" so that filenames are listed from the
404top of the kernel source tree and don't use too much horizontal space
405(easily fit in 80 columns, maybe with some indentation).
Paul Jackson75f84262005-10-02 18:01:42 -0700406
407See more details on the proper patch format in the following
408references.
409
410
Randy Dunlap84da7c02005-06-28 20:45:30 -0700411
412
Linus Torvalds1da177e2005-04-16 15:20:36 -0700413-----------------------------------
414SECTION 2 - HINTS, TIPS, AND TRICKS
415-----------------------------------
416
417This section lists many of the common "rules" associated with code
418submitted to the kernel. There are always exceptions... but you must
419have a really good reason for doing so. You could probably call this
420section Linus Computer Science 101.
421
422
423
4241) Read Documentation/CodingStyle
425
426Nuff said. If your code deviates too much from this, it is likely
427to be rejected without further review, and without comment.
428
429
430
4312) #ifdefs are ugly
432
433Code cluttered with ifdefs is difficult to read and maintain. Don't do
434it. Instead, put your ifdefs in a header, and conditionally define
435'static inline' functions, or macros, which are used in the code.
436Let the compiler optimize away the "no-op" case.
437
438Simple example, of poor code:
439
440 dev = alloc_etherdev (sizeof(struct funky_private));
441 if (!dev)
442 return -ENODEV;
443 #ifdef CONFIG_NET_FUNKINESS
444 init_funky_net(dev);
445 #endif
446
447Cleaned-up example:
448
449(in header)
450 #ifndef CONFIG_NET_FUNKINESS
451 static inline void init_funky_net (struct net_device *d) {}
452 #endif
453
454(in the code itself)
455 dev = alloc_etherdev (sizeof(struct funky_private));
456 if (!dev)
457 return -ENODEV;
458 init_funky_net(dev);
459
460
461
4623) 'static inline' is better than a macro
463
464Static inline functions are greatly preferred over macros.
465They provide type safety, have no length limitations, no formatting
466limitations, and under gcc they are as cheap as macros.
467
468Macros should only be used for cases where a static inline is clearly
469suboptimal [there a few, isolated cases of this in fast paths],
470or where it is impossible to use a static inline function [such as
471string-izing].
472
473'static inline' is preferred over 'static __inline__', 'extern inline',
474and 'extern __inline__'.
475
476
477
4784) Don't over-design.
479
480Don't try to anticipate nebulous future cases which may or may not
Randy Dunlap84da7c02005-06-28 20:45:30 -0700481be useful: "Make it as simple as you can, and no simpler."
Linus Torvalds1da177e2005-04-16 15:20:36 -0700482
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800483
484
485----------------------
486SECTION 3 - REFERENCES
487----------------------
488
489Andrew Morton, "The perfect patch" (tpp).
490 <http://www.zip.com.au/~akpm/linux/patches/stuff/tpp.txt>
491
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700492Jeff Garzik, "Linux kernel patch submission format".
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800493 <http://linux.yyz.us/patch-format.html>
494
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700495Greg Kroah-Hartman, "How to piss off a kernel subsystem maintainer".
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800496 <http://www.kroah.com/log/2005/03/31/>
497 <http://www.kroah.com/log/2005/07/08/>
498 <http://www.kroah.com/log/2005/10/19/>
Xose Vazquez Pereze1b114e2006-01-14 12:57:41 +0100499 <http://www.kroah.com/log/2006/01/11/>
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800500
Randy Dunlapbc7455f2006-07-30 03:03:45 -0700501NO!!!! No more huge patch bombs to linux-kernel@vger.kernel.org people!
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800502 <http://marc.theaimsgroup.com/?l=linux-kernel&m=112112749912944&w=2>
503
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700504Kernel Documentation/CodingStyle:
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800505 <http://sosdg.org/~coywolf/lxr/source/Documentation/CodingStyle>
506
Pavel Machek8e9cb8f2006-09-29 02:01:29 -0700507Linus Torvalds's mail on the canonical patch format:
Xose Vazquez Perez5b0ed2c2006-01-08 01:02:49 -0800508 <http://lkml.org/lkml/2005/4/7/183>
509--